AR-15 Bolt Issue?

[G11354]

My rifle is a Smith & Wesson M&P15 chambered in 5.56mm. Been having issues with the bolt not catching the first round when released and not locking open after the last shot.
Shoots just fine, no jams or other obvious issues.

Been shooting hand loads and some factory loads. Seems more common with hand loaded rounds. Hand loads contain 22.2 gn and 22.3 gn of IMR 3031, was experimenting with different charges.

I have used three different magazines and experienced this issue with them all.

Any input would be greatly appreciated.

 

[W.E.G.]

What magazines are you using?

When you push on the bottom of the magazine, does the problem go away?

 

[G11354]

I am using a 30 round Magpul P-Mag and a 20 round Colt magazine. Oddly enough I never gave the mag a push, I removed it and then put it back in.

Still I cant see how it would fail to lock open on a dry mag after firing flawlessly.

 

[taliv]

gas guns are finicky about propellant burn rates. a load that shoots spectacularly in a bolt gun might not cycle a gas gun properly, even if the bullet is around the right velocity.

if factory shoots fine, try changing powders, or at least researching it and making sure that one is acceptable. i don't know anyone else trying to use that powder in an AR15.

varget, WC844, A2230, H335, N540 are all popular AR15 powders

 

[W.E.G.]

Not picking up the first round impresses me as a very different problem than not locking back on last round. You need to eliminate the possibility that the mag is riding too low in the gun.

That's why I asked about the magazines and about whether pushing on the bottom of the magazine makes any difference.

It is worth investigating to determine whether pressure on the bottom of the magazine has any effect on picking up the first round.

Not locking back on the last round could also be an issue with a too-low mag, but it seems like that override issue would be present on EACH round, and not just on the last round if the too-low mag were in play.

20-round PMAG's have a well-documented issue with not picking up the first round when loaded from a CLOSED BOLT. I have tried to duplicate the problem with 30-round PMAG's, and have not been able to cause a malfunction loading from the closed bolt.

You mentioned the powder charge, but you omitted the bullet weight.
What bullet weight are you using on your handloads?

 

[G11354]

Using 60 gn Hornady V-Max.

 

[col.lemat]

I have been using 26gr. of 3031 with 55gr. bullets for 45 years. Never had any troubles .

 

[G11354]

Im thinking I have a bad set of magazines, I'll load up 50 or so rounds and try my luck again.

Thank you all for the assistance, I greatly appreciate it!

 

[W.E.G.]

Using 60 gn Hornady V-Max.

IMR 3031 is a poor powder choice.
Too slow for the 5.56

Very underpowered load even at 104% loading density.

I don't know whether you have a gun issue.
I can guarantee you have an ammo issue if you expect that load to cycle correctly in an AR15.

 

[KansasPaul]

W.E.G - that software program looks awesome.

OP - I too think that a powder change is in order. I've had good luck with H335, BLC-2 and Varget. Varget is my preferred powder because it exhibits consistent velocities regardless of ambient temperature.

Paul

 

[rcmodel]

IMR 3031 is a poor powder choice.
Too slow for the 5.56

IMR 3031 is too fast and too bulky for the .223/5.56 with a 60 grain bullet.

I don't care what Quick-Load says it is.

BTW; Hodgdon load data says 20.6C is a max charge giving 48,700 PSI..

So how do you get 22.3 grains to fit??

rc

 

[taliv]

am i reading that right? does it say 22.3g of 3031 uses 104% case capacity (presumably, that's the volume of the case after subtracting the volume of the projectile)

if so, col.lemat's 26g must get pretty crunchy!

 

[G11354]

22.3 gn does not compress powder.

 

[alsaqr]

I have been using 26gr. of 3031 with 55gr. bullets for 45 years. Never had any troubles .

Bingo!!!

25.5 grains of IMR 3031 and any 55 grain bullet has worked for me since 1968.

 

[taliv]

i guess that's not what that field means then. out of curiosity, are those compressed loads?

col.lemat and alsaqr, what rifle are you shooting those in? what gas length? (20" bbl and rifle gas since you're shooting since the 60s?)

 

[alsaqr]

col.lemat and alsaqr, what rifle are you shooting those in? what gas length? (20" bbl and rifle gas since you're shooting since the 60s?)

Two Stag Arms AR-15 models, one with a 20" barrel the other with a 16" barrel, and two 60s model Colts with 20" barrels. i also fired those reloads from a Heckler and Koch while i owned it. Never had a bauble with my reloads in any of my guns.

The last printed Du Pont reloading manual lists 25 grains as maximum load using a Remington case and a 55 grain Hornady spire point bullet. The 1972 Hornady reloading handbook lists 24.7 grains as maximum when using a Remington case and a 55 grain Hornady bullet. Hornady tested that load in the Colt AR-15. Did a lot of load workup and was able to safely exceed the loads now listed as maximum in my current rifles.

Most of my reloads use military cases. i have two 32 gallon garbage cans full of once fired mostly LC and TW cases. Using a US military case, compression starts at over 24 grains. The monolithic bullets like Barnes TSX are longer and require deeper seating: i reduce the powder charge when reloading them for my AR-15 guns.

 

[W.E.G.]

Where the chart reads" "Filling/L.R." that refers to whether the powder charge uses all the available space in the case after the prescribed bullet is seated.

104% would be a mildly compressed load.

 

[W.E.G.]

rc is correct that I should not have characterized IMR3031 as "slow" powder.

Well, at least not so long as we go by "the chart."
http://www.reloadbench.com/burn.html

This where we have to be careful when we we start getting into the bulk vs. volume vs. burn-rate issues.

IMR3031 fills up a 5.56 case quickly.
And please note that we are using 5.56 pressure specs.
62366 PSI is the limit for 5.56 --- NOT 48700 PSI
We are talking 5.56 caliber AR15's here.
If somebody wants to talk early-70's bolt-gun .223's we can do that another time.

IMR3031 as noted by rc is a "fast" powder by weight.
The problem is, it is a SLOW powder by volume.
This is why the OP is at 104% loading density, but still coming up short on pressure and velocity.
So, I think rc and I are really saying the same thing, but using different observations to get there.

With the OP's 22.3 charge-weight, but substituting TAC, a significantly "slower" powder if you go by "the chart,"
we only fill the case 91%.



When we fill the case only to 99% loading-density with this "slower" TAC powder, we get nearly 100 fps MORE velocity
than the OP's 3031 load because TAC packs more power by volume.

 

[Walkalong]

Yep, Tac is much better suited, as are other similar powders, both in burn rate and volume per Gr of weight.

 

[col.lemat]

Colt AR15 Ser.# very low 6,100 range. Bought secound hand in summer of 1966. I worked my tail off the summer I graduated to buy that thing for $175 First gun I ever reloaded for. The dies cost all of $8. from an RCBS jobber. Ther was no data in those days and I started with 21gr.((used data for 222as Jobber sugested) and worked it up over the years. The military crimp was something to learn about as it gave me fits. I used a drill to remove it in desperation. I like using 3031 as I can not double charge + use it for 7.62MM & 30/06. Ammo if you could find it was 10 cents a round while 30 cal. was a nickle, carbine was 3 cents. My dad had a cow and threatened to make me return the rifle until he fired it and compaired it to what was a new rifle in his day, the M1. Thirty years later he finally said it was a much better rifle.

 

[W.E.G.]

I'm kind of the same way - but with Varget.

Just a bit too bulky for 5.56, but gets the job done if you don't mind a little crunch.
Works just fine with the .308 and the 30-06.

And the stuff is so darn easy to find when I'm in a powder buyin' mood.

I'm trying to cull my powder inventory down to 231, Unique, and Varget.

 

[G11354]

Took the rifle out to the range today and experienced no issues on 4 different magazines.

Used same ammunition-
Hornady 60 gn bullet
22.2 gn IMR 3031
Along with some Federal 55 gn 5.56 M193 Ball rounds. No issues.

Made a point to tap bottom of mag while in rifle prior to firing.

Switched gun oil from "Hoppes Elite" to "CLP Break Free".

Thank you all for your input!

 

[hentown]

IF you were using Mobil 1, you'd get even better lubricity, and it won't cook off like the thin, so-called firearms "specialty" oils will. I believe you've solved your problem. I use ball powders, exclusively, that require around 23-25 grains for 55-grain bullets, e.g., H335, AA2200, AA2230, 844. In thousands of rounds of my reloads, I've never had a failure to function with one of my ARs.